If you have read that the gaokao is 'six subjects', you have read about the 3+1+2 model, the version of China's reformed university entrance exam (the 'new gaokao', 新高考) now used in many provinces. The name describes how a candidate's subjects are made up.
The '3' are compulsory for everyone: Chinese (语文), mathematics (数学) and a foreign language (外语), each worth 150 points. The foreign language is usually English, but candidates may also choose Japanese, Russian, French, German or Spanish.
The '1' is a choice between physics (物理) and history (历史). It is called the first-choice subject (首选科目), and it matters twice over: it is counted at its raw score, and it decides which admission group the student belongs to. Universities publish separate enrolment plans and separate cutoff scores for the physics group and the history group.
The '2' are two subjects chosen from chemistry, biology, geography and politics (思想政治). These re-elected subjects (再选科目) are not counted at their raw score. Instead they are converted through a rank-based system called 等级赋分: candidates are ranked within the province, placed in grade bands, and given a converted score. The exact bands are set province by province.
Each elective is worth 100 points, so the total is 150 x 3 + 100 x 3 = 750. Combining one of two first-choice subjects with two of four others gives twelve possible combinations, from physics-chemistry-biology to history-politics-geography.
Why it matters: universities state which subjects each major requires. Most engineering, science and medical programmes require physics, and many also require chemistry, while humanities programmes are usually open to both groups. Students make their choice around the start of senior high school, so the decision shapes their options years before they apply.
The model was introduced in a first group of eight provinces and municipalities (Hebei, Liaoning, Jiangsu, Fujian, Hubei, Hunan, Guangdong and Chongqing) and has since spread to many more. Shanghai, Zhejiang and a few others use a related '3+3' model instead. Because rules, timetables and score conversion differ by province and change over time, the provincial examination authority is always the final reference.